Gas-permeable, liquid-impermeable vents find use in many applications in the automotive industry, such as, electrical component housings, gear housings, vehicle bodies, brake housings, etc. where pressure equalization between the housing interior and surrounding environment must occur. These gas pressure equalizing vents can also be used in electrical equipment housings. While vents must allow for gas pressure equalization, they must also seal the interior of the housings from moisture and/or liquids. Failure to exclude moisture and liquids, such as water, can damage the components and corrode the housing.
For example, in German Utility Patent G8707254.8, a gas-permeable, water-impermeable venting assembly for equalizing pressure has been used in a housing that mounts a drive mechanism for a car window or sliding roof. The housing includes a stepped bore with a shoulder for supporting the element that is formed from three separate components. The three component venting assembly includes a membrane juxtaposed against the shoulder of the bore and is maintained in sealing engagement by a sealing ring and spring lock washer. The assembly requires separate insertion of each component. Moreover, the degree of sealing is not fully satisfactory and does not protect the membrane surface from contaminating liquids and grease. Also, because the membrane surface is unprotected, damage from impinging and immersing liquids can occur.
An equalizing element formed from a resilient ring having a polytetrafluoroethylene membrane is described in U.S. Pat. No. 5,215,512. The resilient ring is outwardly flared and retained in a shouldered bore of smaller diameter within a gear housing wall. The element is maintained in position by the outward pressure exerted by the outwardly flared ring against the wall of the bore. A polytetrafluoroethylene membrane extends across the open center section of the element. Struts extend across the top of the element and membrane in a spaced apart arrangement. The struts provide minimal protection to the membrane surface because only a small portion of the membrane is covered by the struts. As a result, a majority of the membrane surface is exposed to the surrounding environment. Moreover, the spacing of the struts from the surface of the membrane does not prevent water, dirt, oil or other contaminating fluids from seeping into the space between the membrane and the struts.
Press fitted articles containing a molded body and a porous membrane formed from polytetrafluoroethylene (PTFE), polypropylene or polyethylene are also known and can be used as an air vent device in a breather valve, a filter, a diaphragm device, etc. The press fitted article includes an interiorly positioned member having a membrane with circumferentially located holes that are positioned between rigid resin portions bound together through the circumferentially located holes. This rigid member is encompassed by a soft resin to form the press fitted article. The resulting article may have a circumferentially located groove.
Air pressure equalizing elements are also known and used to compensate for pressure changes due to temperature differences between the air with a housing and the surrounding environment. One such device is a thimble shaped pressure equalizing element for electrical equipment. The side walls of the element are formed from PTFE. Another such device uses an air-transmissive foil of PTFE that is sandwiched under tension between supporting elements. This device includes a perforated cover.
Although these prior art devices provide for air pressure equalization by using a gas-permeable, liquid-impermeable membrane, they are susceptible to contaminating materials such as oils, greases, organic liquids, as well as dirt. In addition, liquid immersion conditions or direct impingement by liquids frequently damages the membrane in the element and prevent its normal operation. Thus, a need exists for a vent that, in addition to providing for air pressure equalization via a vapor-permeable, liquid impermeable membrane, is also capable of maintaining its integrity under more adverse conditions that occur from immersion, direct impingement or contact with contaminating liquids and dirt. The above disadvantages and problems have been overcome by the present invention described below.